An injection is widely used as a method for injecting a drug into a living body. However, since an injection pricks a skin with a needle, a load such as a pain and skin degeneration is given to the administered patient, and this is seriously problematic especially for chronic disease such as diabetes that requires the injection for a long period of time. In addition, when a drug is administered by injection, a needle touches blood, and thus a problem arises such that infection with viral diseases or the like may be caused by accidental piercing of medical personnel. Further, fear of piercing with a needle is a big problem, and especially when the patient is an infant or a child, it frequently gives a mental shock. Moreover, when a rapid drug administration is required, for example, as a treatment at onset of anaphylaxis shock with an injection by a patient himself or a relative of a patient, it is highly possible that the treatment may be delayed by hesitation due to his fear of injection. Furthermore, considering that it is time-consuming to change needles in a situation where a drug has to be injected to an extremely large number of people like vaccination, a method without using a needle is required from the viewpoint of efficiency. Considering these points, needle-less syringes which push a drug from a small hole under high pressure have been developed. However, since the needle-less syringes also open a hole in the skin upon injection, it still has a problem of pain and skin degeneration similarly to the above syringe.
Among the drug administration methods, oral administration is the easiest, but peptide or protein drugs lose effect due to decomposition or denaturing by the action of gastric acid and digestive enzyme when passing through digestive tracts. For example, insulin which is a peptide drug widely used as an anti-diabetic drug is presently difficult to formulate for oral administration as an alternative to the injection. Recently, protein or peptide drugs such as antibodies tend to increase, and development of their administration methods alternative to the injection is important not only for treatment efficiency but also for quality of life (QOL) of patients.
In order to solve the problems such as physical pain, induration at injected site caused by repetitive administration and bacterial contamination, there has been proposed a method which uses insulin-containing fine particles in order that the drug is inhaled so as to be transferred from lungs into the body. Further, it has been proposed that the fine particles are electrically charged to increase delivery efficiency to lungs (Patent Documents 1 and 2). However, the production of fine particles leads to increase of steps, and thus is costly. Also, handling of solid fine particles is more difficult than handling of solutions, and thus a device for the former is also more complicated.
There has been proposed a method in which a solution is sprayed into a mouth so as to inject it into a living body (Patent Document 3). However, its effect cannot be said to be always satisfactory, and further since a gas such as Freon is used, there have been problems of cost and availability due to special consumables. Also, since Freon is one of the greenhouse gases, it is not preferable from the viewpoint of environment.
Electrospray is a means for spraying charged minute droplets of a liquid at high speed toward a counter electrode by applying a high voltage to a spray nozzle so as to collect electric charges at the tip of the nozzle, and passing the solution through the nozzle tip at which electric charges have been accumulated. The electrospray is widely known as, for example, an ionization method for mass analysis. Usually, a test sample to be analyzed is dissolved in a liquid and electrosprayed to perform ionization. Recently, there has been developed a method called desorption electrospray ionization, in which charged droplets generated by electrospray are allowed to hit a surface to mass-analyze the molecules of the surface (for example, Non-Patent Documents 1 and 2). Further, there have been developed methods in which the electrospray is used to coat a foundation or to spray agricultural chemicals (Patent Documents 3 and 4). However, the coating and spraying are nothing but a level of attaching to the surface.
In addition, there has been reported a method in which DNA is transferred into cells utilizing the electrospray. This method, which is one of the gene transfer methods, is a method in which a high voltage is applied to a suspension containing particles so as to spray it onto cells when it is passed through a capillary tip (Patent Document 6). Moreover, there has been developed a method in which whole cells are brought in contact with a substance to be transferred into the cells, the cells are electrosprayed with a liquid free from the substance to be transferred (Patent Document 7). However, the above method is a method for transferring a drug into cells, and is only shown to be capable of transferring a drug into a cell of an embryonic tissue, but there has not been known any method for transferring a drug through mucosa or skin into blood, subcutaneous tissue lymph or the like in the living body of actual animals.    Patent Document 1: Japanese Patent Laid-open (Kohyo) No. H10-501519    Patent Document 2: U.S. Pat. No. 6,696,090 specification    Patent Document 3: U.S. Pat. No. 7,255,102 specification    Patent Document 4: Japanese Patent Laid-open (Kohyo) No. 2003-506472    Patent Document 5: Japanese Patent Laid-open (Kokai) No. H08-275709    Patent Document 6: U.S. Pat. No. 6,093,557 specification    Patent Document 7: International publication No. WO2007/132891 pamphlet    Non-Patent Document 1: J. B. Fenn, M. Mann, C. K. Meng, S. F. Wong, C. M. Whitehouse, Science, 286, p 64-71, (1989).    Non-Patent Document 2: Z. Takats, J. M. Wiseman, B. Cologen, R. G. Cooks, Science, 306, p 471-473, (2004).